1. Field of the Invention
The present invention relates to subsea blowout preventer control pods.
2. Description of the Prior Art
Blowout preventers, referred to in the oil and gas industry as BOPs, are used to prevent blowouts during the drilling and production of oil and gas wells. The BOPs are installed at the wellhead for the purpose of preventing the escape of pressure in an annular space between the casing and drill pipe or in an open hole during drilling and completion operations. On floating offshore rigs, such as semisubmersibles and drill ships, the BOPs are attached to the well on the seafloor.
BOPs are large, high-pressure valves capable of being remotely controlled. There are two basic types of BOPs--annular and ram. Typically, a plurality of BOPs are stacked on top of one another and referred to as a BOP stack. The BOP stack is attached to the wellhead.
Next to the BOPs, the most important well control component is the system that monitors and controls the behavior of the subsea BOPs from the drilling rig. One of the components of the system that monitors and controls the behavior of the subsea BOPs is a subsea control pod. The subsea control pod is adapted to mount to the subsea BOP stack and provide a means of actuating and controlling the subsea BOP stack from the drilling vessel. Hydraulic lines from the drilling rig enter the subsea control pod, and the fluid is directed to the BOPs. The subsea control pod contains pilot operated control valves and pilot operated regulators which direct hydraulic fluids to the various BOP hydraulic operators controlling the BOP functions. Typically, two subsea control pods are used so that, should one fail, the other can be employed.
Subsea control pods are typically of the retrievable type as opposed to the nonretrievable type. The retrievable subsea control pod has a male portion containing the pod valves, regulators, and hose bundle junction box. The retrievable control pod can be retrieved if there are malfunctions of the pod valves, regulator or hose bundle without retrieving any additional equipment.
The retrievable male portion of the control pod is latched into the subsea female portion by hydraulic latching or jacking means. The retrievable male portion and the female portion of the subsea control pod include fluid ports which align and seal with one another when the male and female portions of the subsea control pod are mated. The fluid ports provide the hydraulic passageways for actuating the functions on the BOP stack. Typically, the fluid ports of the male and female portions of the control pod are exposed to the seawater when the portions are not mated. The intrusion of the saltwater into the BOP stack hydraulic operators and the control pod results in corrosion and galling of components and detrimentally effects the reliability and integrity of the entire system.
As drilling operations have moved into the harsh deep water environment, subsea system reliability has become of utmost importance. A significant shortcoming of the prior art subsea control pods is their susceptibility to salt water intrusion into the BOP stack hydraulic operators and the pod during testing, running, and retrieval operations.
Another disadvantage of the prior art is that the subsea pods cannot be expanded or reduced to accommodate the operator's specified BOP stack functions. The number of specified functions to be controlled by the subsea pod is dependent on several factors including operator's preference, the type of well, safety, etc.
It is desirable to have a subsea control pod assembly having modular components so that it allows the versatility to be expanded or reduced, as necessary. It is also desirable to have a male and female portion having sealing gate assemblies which prevent saltwater intrusion into the BOP stack hydraulic operators and the control pod during deployment and retrieval of the male portion of the subsea control pod. It is desirable to have the subsea control pod assembly made from materials resilient to the corrosive effects of saltwater and yet be compatible with each other on the galling and galvanic scales.